ARM architecture family Updated 2024-12-15 +Created 1970-01-01
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This ISA basically completely dominated the smartphone market of the 2010s and beyond, but it started appearing in other areas as the end of Moore's law made it more economical logical for large companies to start developing their own semiconductor, e.g. Google custom silicon, Amazon custom silicon.
It is exciting to see ARM entering the server, desktop and supercomputer market circa 2020, beyond its dominant mobile position and roots.
Ciro Santilli likes to see the underdogs rise, and bite off dominant ones.
The excitement also applies to RISC-V possibly over ARM mobile market one day conversely however.
Basically, as long as were a huge company seeking to develop a CPU and able to control your own ecosystem independently of Windows' desktop domination (held by the need for backward compatibility with a billion end user programs), ARM would be a possibility on your mind.
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Flash memory Updated 2024-12-15 +Created 1970-01-01
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Video 1.
The Engineering Puzzle of Storing Trillions of Bits in your Smartphone / SSD using Quantum Mechanics by Branch Education (2020)
Source. Nice animations show how quantum tunnelling is used to set bits in flash memory.
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Symmetric encryption Updated 2024-12-15 +Created 2024-10-12
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Symmetric encryption is a type of encryption where you use a password (also known as a "key") to encrypt your data, and then the same password to decrypt the data.
For example, this is the type of encryption that is used for encrypting the data in our smartphones and laptops with disk encryption.
This way, if your laptop gets stolen, the thief is not able to see your private photos without knowing your password, even though they are able to read every byte of your disk.
The downside is that that you have to type your password every time you want to login. This leads people to want to use shorter passwords, which in turn are more prone to password cracking.
The other main type of encryption is public-key cryptography.
The advantage of public-key cryptography is that it allows you to send secret messages to other people even an the attacker is able to capture the encrypted messages. This is for example what you want to do when sending a personal message to a friend over the Internet. Such encryption is especially crucial when using wireless communication such as Wi-Fi, where anyone nearby can capture the signals you send and receive, and would be able to read all your data if it weren't encrypted.
Easily sending encrypted messages over the Internet is not possible with symmetric encryption because for your friend to decrypt the message in that system, you'd need to send them the password, which the attacker would also be able to eavesdrop and then decrypt the message that follows using it. The problem of sharing a password with another person online is called key exchange.
Advanced Encryption Standard (AES) is one of the most popular families of symmetric encryption algorithms.
OpenSSL is a popular open source implementation of symmetric and public-key cryptography. A simple example of using OpenSSL for symmetric encryption from the command-line is:
echo 'Hello World!' > message.txt
openssl aes-256-cbc -a -salt -pbkdf2 -in message.txt -out message.txt.enc
This asks for a password, which we set as asdfqwer, and then produces a file message.txt.enc containing garbled text such that:
hd message.txt.enc
contains:
00000000  55 32 46 73 64 47 56 6b  58 31 38 58 48 65 2f 30  |U2FsdGVkX18XHe/0|
00000010  70 56 42 2b 70 45 6c 55  59 38 2b 54 38 7a 4e 34  |pVB+pElUY8+T8zN4|
00000020  4e 37 6d 52 2f 73 6d 4d  62 64 30 3d 0a           |N7mR/smMbd0=.|
0000002d
Then to decrypt:
openssl aes-256-cbc -d -a -pbkdf2 -in message.txt.enc -out message.new.txt
once again asks for your password and given the correct password produces a file message.new.txt containing the original message:
Hello World!
This was tested on Ubuntu 24.04, OpenSSL 3.0.13. See also: How to use OpenSSL to encrypt/decrypt files? on Stack Overflow.
There is no provably secure symmetric-key algorithm besides the one-time pad, which has the serious drawback of requiring the key to be as long as the message. This means that we believe that most encryption algorithms are secure because it is a hugely valuable target and no one has managed to crack them yet. But we don't have a mathematical proof that they are actually secure, so they could in theory be broken by new algorithms one day.
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